The present invention relates to a method for cleaning or preserving a soft hydrophilic contact lens using an amphoteric surfactant which also serves as a solution preservative.
A number of contact lens cleaner solutions are known in the art. Typically such solutions employ either sorbic acid, thimerosal, chlorhexidine, a polyquaternary germicide, a synthetic antibiotic or a conventional quaternary germicide, such as benzalkonium chloride as a preservative agent. However, these conventional preservatives have drawbacks that tend to restrict their use. For example, sorbic acid characteristically contains formaldehyde residues; thimerosal in some patients acts as an allergy sensitizer, chlorhexidine is relatively toxic; and benzalkonium chloride, over a period of time, will tend to accumulate in soft hydrophilic contact lens materials and tend to release to the cornea to cause eye irritation.
While U.S. Pat. No. 4,046,706 discloses the use of certain amphoteric imidazole surfactants in lens-cleaning solutions, such solutions characteristically also require the presence of a germicidal preservative agent of the type discussed above.
Surprisingly and unexpectantly, it has now been found that, while the instant amphoteric surfactant solutions contain a quaternary nitrogen, they do not appreciably build up or accumulate in conventional hydrophilic soft contact lenses. This is in clear contrast to conventional quaternary germicides, such as benzalkonium chlorides (i.e., alkyl substituted dimethylbenzyl ammonium chloride wherein alkyl is a mixture of C.sub.8 to C.sub.18 alkyl moieties), cetylpyridinium chloride and dodecyl triethanolamine hydrochloride, which tend to accumulate in hydrophilic soft contact lens materials. Moreover, the instant amphoteric surfactants do not tend to accumulate in the eye and are characteristically less irritating than such conventional quaternary germicides.
It is therefore an object of the present invention of overcoming the various drawbacks associated with the use of prior art soft contact lens-cleaning solutions.
It is a further object of the present invention to provide a method for preserving and cleaning soft hydrophilic contact lenses using an effective surfactant and solution preservative amount of the instant amphoteric surfactants.
It is yet a further object of the present invention to provide compositions useful in such methods and their preparation.
These and other objects of the present invention are apparent from the following detailed disclosures.